In the last ten years, the practice of carrying chargeable electronic devices on one's person has become almost universal. These devices include cellular telephones, pagers, personal digital assistants (PDA), global positioning systems, and laptops, to name a few. Most people carry one, and many carry several at a time. To remain operational, all of these devices must be charged on a regular basis. Typically, the chargeable electronic devices are not designed to be plugged directly into an electrical outlet. Instead, these devices have battery chargers specifically designed for the particular device. Not only are the battery chargers for, say, laptops and cellular telephones not interchangeable, but the battery chargers for each model of laptop and each model of cellular telephone cannot be used interchangeably. As a result, a typical home will have many battery chargers, several for each member of the household.
In order not to lose or confuse all of these battery chargers, the owners of the chargeable electronic devices often leave their battery chargers plugged into a power strip in the same electrical outlet at all times, ready to charge their electronic device as needed. This practice results in a steady waste of energy, because, even when the battery charger is not charging a chargeable electronic device such as a cellular telephone, the battery charger draws some electrical power as long as the battery charger is plugged into the electrical outlet. The fact that energy is being wasted by these battery chargers on a regular basis can be readily observed even by someone entirely ignorant of the principles of electrical circuits. You only have to touch the charger on the battery charger, typically a rectangular box encased in plastic, to find that it is warm to the touch because of the energy being drawn from the electrical outlet.
Another way in which electronic devices waste energy is by constantly drawing power into receiver circuits designed to detect signals from remote controllers. Increasingly, electronic devices, such as televisions and stereo systems, include remote controllers, which the users of these devices use to turn on and off and otherwise control their electronic devices. To use a television as an example, even when the television has been turned off, the television's receiver circuit continues to draw power to retain the ability to detect a signal from the television's remote controller to turn the television display back on.
Given the concerns about climate change and other environmental harm, there is a growing awareness of the need to conserve energy. In addition, many people would like to conserve energy for the more immediately practical purpose of reducing their energy bills. For all these reasons, there is a need for a system which prevents battery chargers from consuming energy while not actually connected to a battery pack, but which also gives users the convenience of leaving the battery chargers plugged into the same electrical outlet at all times.
In addition, conserving energy requires changes in consumption behavior, and such changes are only justified if they lead to an actual reduction in energy consumption. However, the home consumer lacks the ability to determine whether changes in behavior are producing savings. Without such data, it is very difficult to justify these changes in behavior. Accordingly, we need an invention to accomplish all these goals.